Typically perforating guns for completion of petroleum producing wells are threaded together using threaded interconnection subs or blast joints, so the perforating guns are oriented together at random. This circumstance typically presents no problem when perforation is being accomplished in vertically oriented well bores for the reason that the charges or perforating elements are oriented horizontally and thus fire horizontally with the charges oriented in random manner for perforation of the well casing to establish flow of production fluid into the well casing.
A significant number of petroleum wells are being drilled and completed at this time where the well bore begins from the earth's surface with its upper portion oriented vertically. The well bore, as it extends downwardly, is then transitioned by a deviated or curved section with its lower or terminal extremity being oriented substantially horizontally and being located within a substantially horizontal petroleum bearing formation. The horizontal lower portion of the well bore can extend horizontally in a petroleum producing formation for many hundreds of feet. In such case, it is desirable to perforate the casing at many locations along a considerable portion of its terminus in the formation. Obviously, single perforating guns can be run into the well bore individually to perforate selected lengths of the well casing, with each of the perforations being oriented horizontally so as to remain well within the confines of even narrow petroleum producing zones. Individual, sequential running of perforating guns in this manner is an extremely expensive type of well completion operation. To minimize the "trips" or sequences of well perforation and to accomplish perforation of significant lengths of the lower terminus of the well bore, it is desirable to run multiple interconnected or spaced perforating guns and to fire them simultaneously. Well completion of this manner, however, may require precise orientation of multiple perforating guns because of the requirement for controlled directional firing or shooting. It is desirable, therefore, to provide a means for achieving accurately controlled orientation of multiple perforating guns to thereby enable simultaneous perforation of considerable lengths of well casing in the horizontal portions of well bores.
Controlled directional firing or shooting is important when perforating for a dual completion, when the gun is run in next to the long string blast joint , and the shots must be oriented away from the long string and toward and in close proximity with the well casing. In the alternative, when perforating the casing of a horizontal well, the direction of shooting or firing may need to be restricted solely to horizontal firing, to avoid a water producing zone located above or below the hydrocarbon zone. It is desirable, therefore, to provide a mechanism for achieving accurate orientation of tubing conveyed perforating guns so as to precisely insure that the perforation shots will be oriented with a high degree of directional accuracy.
Most standard tubing conveyed perforating guns are provided with an orienting slot machined on the inside, to orient the loading tube inside the gun. The loading tube carries the perforation charges, so the position of the indexing slot fixes the position of the charge, and thereby, the direction of the perforation that is capable of being achieved upon firing of the gun. When multiple tubing conveyed perforating guns are employed simultaneously, it is desirable to achieve precision orientation of each of the guns relative to the tubing string and with respect to one another. When all of the perforating guns are oriented with a high degree of precision, then the direction of firing of each of the guns can be accurately controlled and thus each of the perforation shots being fired will be oriented specifically with respect to the petroleum bearing formation being completed for production.